Here is a conversion chart. I think most will agree you should be somewhere between 7 - 10 dKH.

http://www.saltwaterfish.com/vb/showthread.php?t=175205

Hmm, just a thought... how did you acclimate your crabs when you added them to the tank? Did you drip acclimate over the course of a couple hours? If you didn't slowly acclimate them, that is likely the cause of their death rather than some off parameter.

I really want porcelain crabs in my tank but they don't seem to survive.

I tried one from big als first,
after the drip for 3 hours it died within about 2 hours of being in the tank

then on my second attempt i bought 3 thinking it was maybe an unlucky crab and dripped for longer. One died in the drip chamber, the other two died after about 2 days.

definitely something abotu my water conditions that is killing the crabs.

I'm gonna invest in a slew of new test kits to get a better idea of what's going on with my tank.

Salifert are a good quality test kit and a bit cheaper than Elos. I much prefer the Salifert alkalinity kit to the Elos one as well.

My alkalinity is

2 meq/L!

that looks low according to everything I"ve read. Any ideas on how to fix this?

By using this calculator: http://reef.diesyst.com/chemcalc/chemcalc.html

For a 30 gal tank dissolve 2 tsp of baking soda in water (I use RO/DI) to boost your alkalinity from 2 meq/lt to 3meq/lt

Dont add the solution all at once to your aquarium, add a little at a time perhaps over a day and keep an eye on your pH if you can.

Temp flux may start to cause havoc in smaller tank esp. Check in the morning and after the lights go out and see how wide the flux of temp is esp of a hotter day. Make sure you thermometer is accurate many are way off. You can pull it and cross check it with your home thermostat. Just another thing to check. Your salinity and how are you measuring it ?

therm is good (just checked)

and salinity with a refractometer.

+1 on the salifert kits i like using them too easy to use. i have never had any problems with them ever since using them....
I also know that a sudden drop in ALk will cause you SPS to die too... that may have been your problem too, any sudden change in Temp by chance, or PH

Hi
Usually a change in alkalinity may cause that problem. What is your alk?
Another direction is a change in salinity or in temperature. In my experience some folks damage their system during water changes without proper equalization.

I have also noticed your ca is on the low side and you don’t have an ALK and MG test results. If you can provide dose it will help diagnosing you problem.

When you touch you sps corals do they brake easily?